Re: [PATCH v2] failover: specify an alternate MAC address

[Philippe Mathieu-Daudé]

On 10/27/21 11:59, Laurent Vivier wrote:
> If the guest driver doesn't support the STANDBY feature, by default
> we keep the virtio-net device and don't hotplug the VFIO device,
> but in some cases, user can prefer to use the VFIO device rather
> than the virtio-net one. We can't unplug the virtio-net device
> (because on migration it is expected on the destination side) but
> we can keep both interfaces if the MAC addresses are different
> (to have the same MAC address can cause kernel crash with old
> kernel). The VFIO device will be unplugged before the migration
> like in the normal failover migration but without a failover device.
> 
> This patch adds a new property to the virtio-net device:
> "failover-legacy-mac"
> 
> If an alternate MAC address is provided with "failover-legacy-mac" and
> the STANDBY feature is not supported, both interfaces are plugged
> but the standby interface (virtio-net) MAC address is set to the
> value provided by the "failover-legacy-mac" parameter.
> 
> If the STANDBY feature is supported by guest and QEMU, the virtio-net
> failover acts as usual.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
> 
> Notes:
>     v2: rename alt-mac to failover-legacy-mac
>         update doc with text provided by MST
> 
>  docs/system/virtio-net-failover.rst | 10 ++++++
>  hw/net/virtio-net.c                 | 48 +++++++++++++++++++++++------
>  include/hw/virtio/virtio-net.h      |  6 ++++
>  3 files changed, 55 insertions(+), 9 deletions(-)

> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index f2014d5ea0b3..0d47d287de14 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -45,6 +45,9 @@
>  #include "net_rx_pkt.h"
>  #include "hw/virtio/vhost.h"
>  
> +/* zero MAC address to check with */
> +static const MACAddr zero = { .a = { 0, 0, 0, 0, 0, 0 } };
> +

Eventual future cleanup, it might be clearer to declare it extern
in "net/net.h" and use the one in qemu_macaddr_default_if_unset().